Opt into saved billing information separately from account creation

For GiveCampus accounts and administrator access.

For an ordinary signed-in Stripe card gift, the checkout offers an unchecked Save my billing info for one-click donations checkbox. Leave it unchecked to enter a card for that gift without opting into the reusable account wallet; a saved method is not required merely because an account exists, and the checkout also offers a new-card option. Match/challenge commitments explicitly save a method for later processing, and recurring commitments need a payment source for future charges. Wallet opt-out does not erase gift/transaction records or processor retention; third-party wallet enrollment such as Stripe Link has its own controls.